1. Field of the Invention
The present invention relates generally to the field of information storage devices, and more particularly to the magnetic random access memory (MRAM) devices and thermal properties associated therewith.
2. Description of the Related Art
Magnetic Random Access Memory, or MRAM, is a non-volatile memory that may be employed for both short term and long term data storage. One implementation of an MRAM device includes a resistive cross point array of spin dependent tunneling (SDT) junctions, with word lines extending along rows of the SDT junctions and bit lines extending along the columns of the SDT junctions. Each SDT junction is located at a cross point of a word line and a bit line. The magnetization of each SDT junction assumes one of two stable orientations at any given time. These two stable orientations, parallel and anti-parallel, represent logic values of ‘0’ and ‘1.’ The magnetization orientation, in turn, affects the resistance of the SDT junction. Resistance of the SDT junction is a first value (R) when the magnetization orientation is parallel and a second value (R+ΔR) when the magnetization orientation is anti-parallel. The magnetization orientation of the SDT junction and its logic value may be read by sensing its resistance state.
An MRAM using the foregoing SDT junction design performs a write operation on a selected SDT junction by supplying write currents to the word and bit lines crossing the selected SDT junction. The currents create two external magnetic fields that, when combined, switch the magnetization orientation of the selected SDT junction from parallel to anti-parallel or vice versa.
Too small a write current might not cause the selected SDT junction to change its magnetization orientation. In theory, both external fields combined should be sufficient to flip the magnetization orientation of the selected SDT junction. In practice, however, the combined magnetic fields do not always flip the magnetization orientation. If the magnetization orientation of the selected SDT junction is not flipped, a write error is made and an increased burden on error code correction can result.
Heating the MRAM to enable thermally assisted switching of the MRAM device may assist in performing the write operation. Different procedures for heating the MRAM cell have been employed with varying effectiveness. One such method comprises heating the entire MRAM using an external heat source. Problems with this heating method include nonselective heating, including heating components that do not enhance thermal assisted switching and the write process. An external heater is not practical for many applications, and typically requires very high external temperatures. Thermal time constants associated with external heating also tend to be relatively long, resulting in slow overall operation of the device.
Other memory architectures encounter self heating when the system selects the particular cell. However, the magnitude of the power generated from self-heating is generally insufficient to enhance the write operation in any material way. A more significant voltage drop across the selected MRAM cell may enhance writing.
It would be advantageous to provide efficient heating of SDT junction MRAM memory cells, specifically heating that efficiently enhances writing capabilities and avoids the problems associated with previous designs.